feat(core): plumb distinct approval ids for command approvals (#12051)

zsh fork PR stack:
- https://github.com/openai/codex/pull/12051 👈 
- https://github.com/openai/codex/pull/12052

With upcoming support for a fork of zsh that allows us to intercept
`execve` and run execpolicy checks for each subcommand as part of a
`CommandExecution`, it will be possible for there to be multiple
approval requests for a shell command like `/path/to/zsh -lc 'git status
&& rg \"TODO\" src && make test'`.

To support that, this PR introduces a new `approval_id` field across
core, protocol, and app-server so that we can associate approvals
properly for subcommands.

codex-rs/app-server-protocol/schema/json/EventMsg.json

@@ -1452,8 +1452,15 @@
         },
         {
           "properties": {
+            "approval_id": {
+              "description": "Identifier for this specific approval callback.\n\nWhen absent, the approval is for the command item itself (`call_id`). This is present for subcommand approvals (via execve intercept).",
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "call_id": {
-              "description": "Identifier for the associated exec call, if available.",
+              "description": "Identifier for the associated command execution item.",
               "type": "string"
             },
             "command": {
@@ -6392,8 +6399,15 @@
     },
     {
       "properties": {
+        "approval_id": {
+          "description": "Identifier for this specific approval callback.\n\nWhen absent, the approval is for the command item itself (`call_id`). This is present for subcommand approvals (via execve intercept).",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "call_id": {
-          "description": "Identifier for the associated exec call, if available.",
+          "description": "Identifier for the associated command execution item.",
           "type": "string"
         },
         "command": {